The main objective of this proposed research is to understand how cardiac adenylyl cyclase activity is regulated by hormones and other factors. New methods for measurement of adenylyl cyclase activity will be utilized to analyze important kinetic and physical parameters of this activity in particulate and solubilized preparations of cat heart adenylyl cyclase. As an important step towards the above main objective, we are proposing an in depth investigation of the mechanism by which pyruvate acts to stimulate the soluble adenlyly cyclase obtained from Brevibacterium liquefaciens. This investigation will include the purification of this enzyme and a detailed analysis of its structure, our hope being that we can apply the insights gained from this study to a better understanding of the more complex system present in mammalian cardiac muscle. We also plan to apply recently developed membrane isolation procedures (based on glass permeation and affinity chromatography) to the problem of separating cardiac membrane complexes containing hormone receptors (beta adrenergic receptors and glucagon receptors) linked to adenylyl cyclase activity. The results of this study should lead to an improved understanding of he regulation of cardiac function by hormones. The undersinged agrees to accept responsibility for the scientific and technical conduct of the project and for the provision of required progress reports if a grant is awarded as the result of this application.